In this last case, the wings are invisible to everyone and are sensed as solid and vast only by Rudi, whose inner experience continues:

"He felt as if his blood had been replaced with something that scalded and froze at the same time, like boiling acid." (ibid.)

Either the Gods favor Rudi or he is particularly prone to this kind of experience. Some people see things. Whether or in what sense what they see exists is a complicated question that I tried to discuss here.